NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Why there was No Lunars Era
From: Alexandre Eremenko
Date: 2004 Dec 7, 15:03 -0500
From: Alexandre Eremenko
Date: 2004 Dec 7, 15:03 -0500
The original question of Frank was (as I understand it) why there was no Lunars era? We were explained that there WAS a Lunars era in the LAND navigation, so it remains to find out why there was no Lunars era in marine navigation. My first guesses were: a) low precision (because of difficulty of measuring distances better than 1') and b) difficulty of reduction These guesses were refuted. I accept this, and will return to this in the end of this message. Here is my second guess. Roughly speaking "Who cares about longitude in marine navigation?" I apologise in advance: I mean European and N American marine navigation (not the Polynesian, Chinese or African ones). In the seas like Black sea or even Mediterranean and Baltic you can probably do well enough with DR only. In the coastal waters ("cabotage") no CelNav is needed if you gave good maps. So we are talking of ocean crossings. But most of the ocean crossings occur E to W (or W to E) don't they? So it is enough to know your latitude to reach the point you want in a typical ocean crossing. One supporting argument is that there were very many successfull ocean crosings before the "Longitude problem" was solved:-) One interesting exception is polar navigation in the "NW passage". I combed the Franklin notebooks on this subject. He mainly used chronometers, though occasional lunars were mentioned too. This is the main part of my message. Now about the refutation of a) and b) in the beginning. 1. My complains about difficulty of reduction were mostly based on a misunderstanding. My misunderstanding. I have no horizon. I had to compute altitudes every time I reduced my lunars. Which I did with the usual formulas and a calculator. Of course if you subtract this labor a lunars computation becomes much easier. 2. Precision. Those members of the list who replied my questions say essentially that they can measure distances to 0.3', and get such results on a regular basis. So far I can do it only to 0.6' on a regular basis, but they say one needs at least 10 years experience to measure the distances well on a regular basis, so I still have 9.5 years to practice:-) My main problem is in determining precisely when do two discs touch. This is the sort of problem which is "hard to address in words" as Bill noticed once. Alex.